The present disclosure relates generally to cardiac implant systems and, more particularly, to a cardiac imaging system and method for planning atrial fibrillation intervention.
Atrial fibrillation (AF) is an arrhythmia in which the atria (upper chambers of the heart) stop contracting as they fibrillate, and is the most common of heart rhythm problems. It is estimated that over 2.2 million Americans have AF. Because of the role of the pulmonary veins (PVs) in generating AF, a variety of surgical and catheter techniques have been used to isolate the PVs from the left atrium using energy sources such as radiofrequency (RF) energy. In addition to PV isolation, several other strategic targets, such as the mitral valve to left inferior PVs, can be targeted to improve efficacy. Transmural lesions formed during ablation are advantageous, as discontinuous lines may allow AF breakthrough or potential development of other arrhythmias such as atrial flutter.
In unipolar systems, where the patient is grounded by an indifferent electrode applied to the skin (usually the back), current flows from the tip of the RF catheter and resistively heats tissue at the catheter tip contact. Deeper tissue planes are heated by conduction from the region of volume heating. Locally, temperatures above 100″ C can occur causing tissue vaporization and surface charring which could be disastrous in areas such as the inside of the PVs. RF current producing temperatures from about 70to 80″ C result in lesions about 3 to 6 mm deep. However, even temperatures above 50″ C are also likely to cause PV stenosis. In studies of the anatomy of the PVs, a significant diversity of muscle fiber orientation is seen around the PVs. It is generally not known how muscle thickness varies in other strategic areas such as the mitral valve to left inferior PVs.
In a typical AF ablation procedure, the location(s) of premature atrial beats which act as triggers for initiation of AF is identified. However, such identification is possible in only a few patients. Then, circular catheters with multiple electrodes are placed inside the PVs. Using a second catheter, the ablation is then performed at sites suggesting conduction between the left atrium (LA) and the PVs. In addition to the previously mentioned problems, additional problems associated with AF ablation include the complex 3D geometry of the left atrium and PVs, as well as the variable muscle thickness and orientation of fibers in and around the PVs. These features make it difficult to appropriately target the areas of interest. As such, it would be desirable to be able to provide information, such as muscle thickness at and around the pulmonary veins and other strategic locations to improve the efficacy of an AV ablation procedure.